Possible false-negative results on therapeutic drug monitoring of phenytoin using a particle enhanced turbidimetric inhibition immunoassay in a patient with a high level of IgM.

: In this report, the authors described the unusual case of a patient in whom the plasma phenytoin concentration was unexpectedly not detected on a particle-enhanced turbidimetric inhibition immunoassay (PETINIA) technique, a typical immunoassay for phenytoin. The plasma concentration was measured using PETINIA and high-performance liquid chromatography in a 69-year-old male patient treated with fosphenytoin intravenously at the standard dose for 7 days. Although the plasma concentration of phenytoin was below the limit of detection (<0.5 mcg/mL) on PETINIA after the administration of fosphenytoin, the trough plasma concentration was estimated to be between 5 and 10 mg/L on high-performance liquid chromatography. When the plasma concentrations of IgM and IgG were measured using an enzyme-linked immunosorbent assay, the plasma IgG level was within the reference range, whereas the plasma IgM level was 2-3 times higher than the upper limit of the reference range. We concluded that the PETINIA method yielded a possible false-negative result regarding the phenytoin level in this patient, perhaps because of some hindrance to the measurement process by IgM. This case suggests that false-negative results should be considered when therapeutic drug monitoring reveals abnormally low values using PETINIA and that it is necessary to evaluate the plasma IgM level.

Effects of genetic variants in SLC22A2 organic cation transporter 2 and SLC47A1 multidrug and toxin extrusion 1 transporter on cisplatin-induced adverse events.

BACKGROUND: Susceptibility to cisplatin (CDDP) nephrotoxicity is known to vary between individuals, but the basis of this variation has not been fully elucidated. In the kidney, CDDP is taken up into the renal proximal tubular cells mainly via SLC22A2 organic cation transporter 2 (OCT2) and secreted into lumen via other transporters including SLC47A1 multidrug and toxin extrusion 1 (MATE1). Here, we explore the effect of single-nucleotide polymorphisms (SNPs) at 808G>T in OCT2 and at rs2289669 G>A in MATE1 on CDDP-induced adverse events. METHODS: Fifty-three patients who had been treated with CDDP were enrolled. The plasma concentration of CDDP was measured on days 4 and 7 after treatment. The grade of hematology and nephrotoxicity was evaluated by Common Terminology Criteria for Adverse Events. RESULTS: In the first treatment cycle, serum creatinine (SCr) levels in the patients with OCT2 808GG and 808GT were increased by 1.43- and 1.19-fold, respectively. In the total treatment cycles, 12 patients (27 %) with 808GG experienced over grade 2 SCr elevation, whereas those with 808GT did not show any apparent nephrotoxicity. The hematological toxicity and plasma concentrations of CDDP showed no difference between patients in both groups. The rs2289669 G>A SNP in MATE1 was not associated with adverse effects and disposition of CDDP. CONCLUSION: The 808G>T SNP in OCT2 ameliorated CDDP-induced nephrotoxicity without alteration of disposition, whereas the rs2289669 G>A SNP in MATE1 had no effect on CDDP toxicity.

The relationship between treatment time of gemcitabine and development of hematologic toxicity in cancer patients.

Although gemcitabine is frequently used in the treatment of cancer, it is associated with myelosuppression. An animal study showed that the tolerability of gemcitabine varied with changes in treatment time; however, no clinical data have verified this finding. The purpose of this study was to determine the relationship between treatment time and development of hematologic toxicity in patients treated with gemcitabine. Gemcitabine-induced hematologic toxicity was retrospectively investigated in 77 patients. Patients were divided into two treatment-time groups: 9:00 and 15:00. Hematologic toxicity was evaluated on day 8 and 15 after treatment. On day 8 and 15, the changing count of white blood cells was significantly reduced in patients treated at 15:00 compared with those treated at 9:00 (p<0.01 and p<0.05, respectively). On days 8 and 15, the changing count of platelet was significantly reduced in patients treated at 15:00 compared with those treated at 9:00 (p<0.05). The incident of over common terminology criteria for adverse events (CTCAE) grade 2 white blood cell decreased was significantly reduced in patients treated at 15:00 compared with those treated at 9:00 (p=0.048, odds ratio=2.92). In conclusion, this cohort study demonstrated that gemcitabine-induced hematologic toxicity could be alleviated by treating patients at 9:00.